At least one person has been killed and many others injured in two separate explosions in Russia's North Caucasus region.

An explosion hit a cafe in the city of Pyatigorsk, which lies at the foothills of the Caucasus mountains, injuring at least 20 people on Tuesday afternoon.

Stanislav Belyayev, a spokesman for the Stavropol region police, said the explosion appeared to be a "deliberate terror attack", but added an official investigation was under way.

Earlier in the day a suicide bomber killed one policeman and injured three others in North Ossetia, authorities said.

The attacker blew himself up after approaching a checkpoint on a road near the border with Ingushetia province, a North Ossetian police official said.

"He detonated an unidentified explosive device," Samir Sabatkoyev, a spokesman for the regional interior ministry, told the AFP news agency.

North Ossetia lies to the north of the breakaway Georgian region of South Ossetia, recognised by Russia as independent after the 2008 war with Georgia over its status.

Tuesday's attack took place in North Ossetia's Prigorodny district, the site of a territorial dispute between ethnic Ossetians and Ingush that erupted into fighting in 1992 and remains a source of tension.

The region is also part of the country's volatile North Caucasus, which has seen violence between separatist fighters and Russian forces spread from Chechnya to the neighbouring regions of Dagestan and Ingushetia.

Ongoing violence stems from two separatist wars in Chechnya following the collapse of the Soviet Union in 1991.

But analysts also say poverty and corruption help create a fertile ground for attacks, and help separatists to recruit young people in the region.